High purity copper sulfate and method for production thereof

ABSTRACT

High purity copper sulfate having a purity of 99.99% or higher and in which the content of transition metals such as Fe, Cr, Ni is 3 wtppm or less; and a method for producing such high purity copper sulfate which includes the steps of dissolving copper sulfate crystals in purified water, performing evaporative concentration thereto, removing the crystals precipitated initially, performing further evaporative concentration to effect crystallization, and subjecting this to filtration to obtain high purity copper sulfate. This manufacturing method of high purity copper sulfate allows the efficient removal of impurities from commercially available copper sulfate crystals at a low cost through dissolution with purified water and thermal concentration.

BACKGROUND OF THE INVENTION

The present invention relates to a manufacturing method of high puritycopper sulfate which includes the steps of dissolving commerciallyavailable copper sulfate crystals (purity, for instance, is 95 to 99.9wt %) in purified water, performing thermal concentration thereto, andfiltering out the crystals precipitated initially to eliminate theimpurities, and to the high purity copper sulfate obtained thereby. Thestarting material does not have to be copper sulfate crystal, and may bea material in which copper is dissolved with acid containing sulfuricacid, or copper sulfate crystals manufactured therefrom.

Although copper sulfate (Cu₂SO₄) is white-colored powder, Hydrous coppersulfate (Cu₂SO₄-5H₂O) is the general term thereof, and this is anazurite blue crystal.

Copper sulfate is used as an electrolytic solution, pigment,insecticide, antiseptic, mordant, battery material, pharmaceutical andso on. In particular, when it is to be used as the electroplatingsolution in electronic components such as a semiconductor device, highpurity copper sulfate is being sought.

Commercially available copper sulfate has a purity level of 95 to 99.9wt %, and it is necessary to purify this even further to obtain a levelof 4N to 5N or more.

As conventional technology, described is a method to obtain coppersulfate with low Ni content by using electrolytic copper powderrecovered from an electrolytic solution via electrodeposition as the rawmaterial, immersing this into an acid solution to selectively dissolveand remove Ni, dissolving the filtered copper powder in sulfuric acid,and subjecting this to crystallization (for example, c.f. JapanesePatent Laid-Open Publication No. 2001-10817).

Further, disclosed is technology for obtaining copper sulfate with lownickel content by employing an aqueous solution of copper sulfatecontaining nickel and heating this to 80° C. or higher, collecting thecopper sulfate crystal separated and sedimented, and concentrating thisto effect recrystallization (for example, c.f. Japanese Patent Laid-OpenPublication No. 2001-31419).

SUMMARY OF THE INVENTION

An object of the present invention is to provide a manufacturing methodof high purity copper sulfate which allows the efficient removal ofimpurities from commercially available copper sulfate crystals at a lowcost through dissolution with purified water and thermal concentration,and the high purity copper sulfate obtained thereby.

The present invention provides:

1. A manufacturing method of high purity copper sulfate, including thesteps of dissolving copper sulfate crystals in purified water,performing evaporative concentration thereto, removing the crystalsprecipitated initially, performing further evaporative concentration toeffect crystallization, subjecting this to filtration to obtain highpurity copper sulfate, and performing desiccation thereto;2. A manufacturing method of high purity copper sulfate according toparagraph 1 above, wherein the initial pH of the solution in which thecopper sulfate was dissolved in purified water is 2 to 4, and the pH ofthe solution after removing the crystals precipitated initially is 2 orless;3. A manufacturing method of high purity copper sulfate according toparagraph 1 or paragraph 2 above, wherein 10 wt % or more of the initialcrystal is removed in relation to the initial input;4. A manufacturing method of high purity copper sulfate according to anyone of paragraphs 1 to 3 above, wherein the filtration solution afterthe final filtration is 2 to 40% of the original fluid volume;5. A manufacturing method of high purity copper sulfate according to anyone of paragraphs 1 to 4 above, wherein the desiccation temperature is40 to 100° C.;6. High purity copper sulfate having a purity of 99.99 wt % or higher,and in which the content of transition metals such as Fe, Cr, Ni is 3wtppm or less;7. High purity copper sulfate manufactured with the method according toany of paragraphs 1 to 5 above, wherein a purity is 99.99 wt % or higherand in which the content of transition metals such as Fe, Cr, Ni is 3wtppm or;8. High purity copper sulfate having a purity of 99.99 wt % or higher,and in which the content of Ag, Cl is respectively 1 wtppm or less;9. High purity copper sulfate according to paragraph 7 above, whereinthe purity thereof is 99.99 wt % or higher, and in which the content ofAg, Cl is respectively 1 wtppm or less;10. High purity copper sulfate having a purity of 99.99 wt % or higher,and in which the content of alkali metals such as Na, K and alkalineearth metals such as Ca, Mg is respectively 1 wtppm or less;11. High purity copper sulfate according to paragraph 9 above, whereinthe purity thereof is 99.99 wt % or higher, and in which the content ofalkali metals such as Na, K and alkaline earth metals such as Ca, Mg isrespectively 1 wtppm or less;12. High purity copper sulfate having a purity of 99.99 wt % or higher,and in which the content of Si containing oxide is 10 wtppm or lessbased on Si conversion; and13. High purity copper sulfate according to paragraph 11 above, whereinthe purity thereof is 99.99 wt % or higher, and in which the content ofSi containing oxide is 10 wtppm or less based on Si conversion.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE is a diagram showing the flow of the manufacturing method ofhigh purity copper sulfate.

DETAILED DESCRIPTION OF THE INVENTION

The analytical values of representative impurities of commerciallyavailable copper sulfate are shown in Table 1. Incidentally, by way ofreference, the comprehensive analytical values including otherimpurities are shown in subsequent Table 6.

As shown in Table 1, this copper sulfate contains transition metals suchas iron, nickel, cobalt; and impurities such as Ca, Cr, Al,respectively, in a content of roughly 0.5 to 100 wtppm. Further, inaddition to the above, several wtppm to several ten wtppm of alkalielements such as Na, K; several ten wtppb of impurities of radioactiveelements such as U, Th; and foreign matters such as oxides are alsocontained therein.

This copper sulfate is dissolved with purified water at roomtemperature. When impurities such as organic matter or foreign matterare mixed therein, impurities such as organic matter or foreign matterare subject to filtration and removed by performing active carbontreatment. Thereupon, noble metals such as Ag can also be removed.

When impurities such as organic matter or foreign matter are not mixedtherein, this active carbon treatment does not have to be performed.When undissolved foreign matter exists, this may be removed with afilter cloth or the like, but may also be removed upon removing theinitial crystals in the subsequent process. The initial pH of thesolution in which the copper sulfate was dissolved in purified water ismade to be 2 to 4. The reason the pH of this solution is made to be 2 to4 is to promote the precipitation of initial crystals by ultrafinehydroxides of the copper sulfate being precipitated.

Next, the solution which dissolved copper sulfate or the filtrationsolution which filtrated copper sulfate solution is heated to atemperature of roughly 50 to 100° C., and subject to evaporativeconcentration.

TABLE 1 wtppm Fe Ni Co Ca Cr Al Na K U Th Raw Material 81 4.3 3.5 3.518.1 3.2 13 3.1 0.01 0.02

After evaporative concentration, this is cooled to room temperature, andcrystals are precipitated. These initial crystals contain numerousimpurities, and, although the precipitated crystals are originally of ablue color, since the pH is high at 2 to 4, such crystals present agreen color since they contain hydroxide. Further, numerous impuritiescan be removed as a result thereof. Thereupon, residue of theundissolved impurities can be simultaneously removed.

Moreover, by increasing the level of the foregoing evaporativeconcentration, the solution volume will decrease, the amount of initialcrystals will increase, and the amount of removed impurities willincrease. Nevertheless, when exceeding a certain level, the amount ofremoved impurities will not increase any further.

Thus, it is desirable to delete 10 wt % or more of the initial crystals(low-grade copper sulfate containing impurities) in relation to theinitial input. Further, the lower the purity of the raw material to beused, it is desirable that the amount of initial crystal to be removedis increased.

After filtering and removing the crystals precipitated initially, the pHof the filtration solution is made to be 2 or less. This is to promotethe precipitation of the copper sulfate without precipitating hydroxide.And, this is reheated to a temperature of 50 to 100° C., and subject toevaporative concentration.

Thereafter, this is cooled to room temperature, crystals of the coppersulfate are precipitated, and subject to filtration to obtain highpurity copper sulfate of a blue color.

It is desirable that the filtration solution after the final filtrationis 2 to 40 wt % of the original fluid volume. In other words, thefiltration solution is to be the residual liquid containingnon-crystallized copper sulfate, and the mixing of Na, K and so on whichcould not be removed from the initial crystal into the crystal can beprevented thereby. The desiccation temperature is preferably 40 to 100°C. If the temperature is less than 40° C., this is not preferable sincemuch time will be required for removing the adsorption moisture, and, ifthe temperature exceeds 100° C., this is not preferable since theHydrous copper sulfate adhesive moisture will be removed and the form ofthe copper sulfate will change.

As a result of the foregoing process, the various impurities shown inTable 1 are reduced to 1 wtppm or 0.1 wtppm or less, respectively, andhigh purity copper sulfate having a level of 4N to 5N or more can beobtained.

It is desirable that the content of Ag, Cl in the high purity coppersulfate is 1 wtppm or less, respectively. This is because when coppersulfate is to be used as the plating solution, Ag, Cl will have anadverse effect on the plating, and will be concentrated in the film.

It is desirable that the content of alkali metals such as Na, K andalkaline earth metals such as Ca, Mg in the high purity copper sulfateis 1 wtppm or less, respectively. This is because when copper sulfate isto be used as the plating solution in the manufacturing method of asemiconductor device, it is easily engulfed in the plating coating, andwill have an adverse on the performance of the semiconductor.

Further, it is desirable that the amount of Si (containing oxide andbased on Si conversion) in the high purity copper sulfate is 10 wtppm orless. This is because it will become foreign matter in the platingcoating.

The flow of the manufacturing method of high purity copper sulfateaccording to the present invention is shown in the FIGURE.

EXAMPLES

Examples of the present invention are now explained. Incidentally, theseExamples are merely illustrative, and the present invention shall in noway be limited thereby. In other words, the present invention shallinclude, within the scope of its technical spirit, any and all modes ormodifications other than the Examples of this invention.

250 g of commercially available copper sulfate (Cu₂SO₄-5H₂O) having a[purity] level of 99.9 wt % containing the impurities shown in Table 1was dissolved in 1000 ml of purified water at room temperature.

Next, this was heated at 90° C. to evaporate water in a prescribedamount. Next, this was cooled to room temperature, the initial crystalswere precipitated, and subject to filtration.

The relationship of the amount of filtration solution and the weight ofinitial crystals, as well as the relationship with the content ofimpurities (representatively showing the analytical value of Fe)contained in the ultimately refined material (copper sulfate) are shownin Table 2.

The weight of the initial crystals upon evaporating the filtrationsolution (liquid solution) such that the amount thereof decreases from900 ml to 600 ml increased from 1 g to 80 g together with suchevaporation. Further, the content of Fe impurities decreased from 15 ppmto 0.6 ppm.

Nevertheless, the impurities did not decrease when removing the initialcrystals exceeding 10 wt %, and, since the yield of the copper sulfatewill decrease, it is desirable to remove 10 wt % or more of the initialcrystal in relation to the initial input.

TABLE 2 Solution Weight of Initial Content of impurities Volume (ml)Crystal (g) (Fe) ppm 900 1 15 800 25 3 700 50 0.8 600 80 0.6

Next, the filtration solution of the copper sulfate which improvedpurity obtained by removing the initial 50 g of the crystal in Table 2was reheated at 90° C., and water was evaporated in a prescribed amount.Then, this was cooled to room temperature, the refined copper sulfatecrystal was precipitated, and subject to filtration.

When the evaporation is increased drastically, there is a possibilitythat impurities such as Na and K will be mixed in the refined coppersulfate, and, therefore, evaporation was discontinued midway to obtainresidual liquid.

The amount of filtration solution (solution volume), weight of therefined copper sulfate (Cu₂SO₄-5H₂O) crystal, and the impurities(representatively shown with the Na content) contained in the refinedcopper sulfate crystal are shown in Table 3. As shown in Table 3, thesolution volume after evaporation decreased from 300 to 10 ml, and therefined copper sulfate crystal increased from 150 to 230 g.

Further, the Na content in the refined copper sulfate crystal increasedfrom 0.3 to 1.0 ppm, and, when the refined copper sulfate crystal was230 g, it increased considerably to 5 wtppm. Thus, excessive evaporationis not preferable from the perspective of impurities such as Na, K.Therefore, it is desirable that the filtration solution after the finalfiltration is 2 to 40% of the original fluid volume.

TABLE 3 Solution Weight of Refined Impurities contained in the Volume(ml) Crystal (g) Refined Crystal (Na) ppm 300 150 0.3 200 180 0.3 150200 0.4 100 210 1.0 10 230 5

The analytical values of the representative impurities of the refinedcopper sulfate obtained in the refining process of the foregoing coppersulfate when 300 ml was evaporated in the process of removing theinitial crystal, and this was concentrated to 300 ml in the process ofprecipitating the refined copper sulfate crystal, are shown in Table 4.Incidentally, by way of reference, the comprehensive analytical valuescontaining other impurities of the refined copper sulfate are shown insubsequent Table 7.

As shown in Table 4, the primary impurities are Fe: 0.8 wtppm; Ni: 0.2wtppm; Co<0.1 wtppm; Ca<0.1 wtppm; Cr: 0.1 wtppm; Al: 0.1 wtppm; Na: 0.4wtppm; K<0.1 wtppm; U<0.005 wtppm; Th<0.005 wtppm and Si: 1.5 wtppm,and, as evident upon comparison with Table 1, significant improvement inthe purity has been confirmed with the simple evaporation and filtrationprocesses illustrated in the examples of the present invention.

These impurities are particularly disfavored in the copperelectroplating to be performed to the likes of a circuit or wiring uponmanufacturing a semiconductor device and so on, and the reduction ofthese impurities is extremely effective.

The initial make-up of the electroplating and electroless plating bathwas conducted with this copper sulfate crystal, electrolytic copperplating and electroless copper plating were performed on a semiconductorwafer, and foreign matter (particles) and the embedding characteristicsin the trench were measured. Incidentally, a trench for embedding acopper wiring was formed on the surface of the semiconductor wafer, anda barrier metal formed from TaN was attached to the surface thereof. Anda thin copper layer was attached thereon with sputtering or CVD. Platingwas performed thereto. The results are shown in Table 5.

Incidentally, the composition and plating conditions of theelectroplating and electroless plating bath are as follows.

(Electroplating Bath and Plating Conditions)

As the plating solution, employed was copper sulfate: 20 g/L (Cu);sulfuric acid: 200 g/L; hydrochloric ion: 60 mg/L (Cl); and [additivebrightening agent, surface active agent] (Product Name: CC-1220,manufactured by Nikko Metal Plating): 1 mL/L.

Plating conditions were plating bath temperature: 30° C.; cathodecurrent density: 2.0 A/dm²; anode current density: 2.0 A/dm²; andplating time: 1 (min).

(Electroless Plating Bath and Plating Conditions)

As the electroless plating solution, employed was copper sulfate: 4 g/L(Cu); reducing agent: formaldehyde (37%) 3 mL/L; complexing agent:EDTA-2 Na 30 g/L; additive 1: Bipyridyl 20 mg/L; and additive 2:polyethylene glycol 20 mg/L.

And, plating was performed for 30 minutes at a plating temperature of70° C. and pH of 12.2.

TABLE 4 4-1 wtppm Fe Ni Co Ca Cr Al Refined 0.8 0.2 <0.1 <0.1 0.1 0.1Material 4-2 wtppm Na K U Th Si Refined 0.3 <0.1 <0.005 <0.005 1.5Material

TABLE 5 Amount of Foreign Embedding Plating Method Matter (quantity)Characteristics Examples Electroplating 3 Favorable Electroless Plating1 Favorable Comparative Electroplating 10 Inferior Examples ElectrolessPlating 8 Inferior

Comparative Examples

Commercially available copper sulfate having a level of 99.9 wt %containing the impurities shown in Table 1 was used to performelectroplating and electroless plating under the same conditions as theexamples.

Foreign matter (particles) and the embedding characteristics in thetrench in this case were measured as with Example 1, and the results aresimilarly shown in Table 5. As shown in Table 5, the amount of foreignmatter in both electroplating and electroless plating in the comparativeexamples increased, and the embedding characteristics were inferior.

As shown in Table 5, in comparison to the comparative examples, theamount of foreign matter (particles) in the examples of the presentinvention was extremely small, there were no voids or engulfment offoreign matter, and a plating coating superior in embeddingcharacteristics was obtained.

Accordingly, it is evident that the present invention yields a superioreffect in that impurities can be effectively removed with a low cost bya relatively simple method of dissolving commercially available coppersulfate having a purity level of 95 to 99.9 wt % in purified water andsubjecting this to thermal concentration. And, it has been confirmedthereby that transition metal elements, alkali metal elements andradioactive elements that are often contained in the copper sulfate canbe reduced, and the high purity copper sulfate can be obtainedefficiently.

The present invention yields a superior effect in that high puritycopper sulfate can be manufactured at a low cost as a result ofeffectively removing impurities by dissolving commercially availablecopper sulfate having a purity level of 95 to 99.9 wt % in purifiedwater and subjecting this to thermal concentration.

TABLE 6 RAW MATERIAL OF COPPER SULFATE DENSITY ELEMENT (ppm wt) Li <0.01Be <0.01 B 1 C — N — O Matrix F <0.1 Na 1.3 Mg 0.08 Al 0.35 Si 17 P 2.3S Matrix Cl 8.5 K <0.1 Ca <0.05 Sc <0.01 Ti 0.04 V <0.01 Cr 1.8 Mn 0.02Fe 21 Co 0.01 Ni 0.08 Cu Matrix Zn <0.1 Ga <0.01 Ge <0.05 As <0.05 Se<0.1 Br <0.1 Rb <0.01 Sr <0.01 Y <0.01 Zr <0.05 Nb <0.05 Mo <0.05 Ru<0.05 Rh <100 Pd <0.05 Ag <0.05 Cd <0.1 In Binder Sn <1 Sb <0.5 Te <0.1I <0.1 Cs <0.1 Ba <0.05 La <0.05 Ce <0.05 Pr <0.05 Nd <0.05 Sm <0.05 Eu<0.05 Gd <0.05 Tb <0.05 Dy <0.05 Ho <0.05 Er <0.05 Tm <0.05 Yb <0.05 Lu<0.05 Hf <0.05 Ta <5 W <0.05 Re <0.01 Os <0.01 Ir 1.8 Pt <0.05 Au <0.1Hg <0.05 Tl <0.01 Pb =<1.5 Bi <0.05 Th <0.005 U <0.005

TABLE 7 HIGH PURITY COPPER SULFATE DENSITY ELEMENT (ppm wt) Li <0.01 Be<0.01 B 0.04 C — N — O Matrix F <0.1 Na 0.4 Mg <0.01 Al 0.1 Si 1.5 P 0.1S Matrix Cl 0.8 K <0.1 Ca <0.1 Sc <0.01 Ti <0.01 V <0.01 Cr 0.1 Mn 0.03Fe 0.8 Co <0.01 Ni 0.2 Cu Matrix Zn 0.1 Ga <0.01 Ge <0.05 As <0.05 Se<0.1 Br <0.1 Rb <0.01 Sr <0.01 Y <0.01 Zr <0.05 Nb <0.05 Mo <0.05 Ru<0.05 Rh <100 Pd <0.05 Ag <0.05 Cd <0.1 In Binder Sn <1 Sb <0.5 Te <0.1I <0.1 Cs <0.1 Ba <0.05 La <0.05 Ce <0.05 Pr <0.05 Nd <0.05 Sm <0.05 Eu<0.05 Gd <0.05 Tb <0.05 Dy <0.05 Ho <0.05 Er <0.05 Tm <0.05 Yb <0.05 Lu<0.05 Hf <0.05 Ta <5 W <0.05 Re <0.01 Os <0.01 Ir <0.05 Pt <0.05 Au <0.1Hg <0.05 Tl <0.01 Pb =<0.7 Bi <0.05 Th <0.005 U <0.005

1. A high purity copper sulfate prepared by a process comprising thesteps of dissolving copper sulfate crystals in purified water,performing evaporative concentration thereto, removing the crystalsprecipitated initially, performing further evaporative concentration toeffect crystallization, subjecting this to filtration to obtain highpurity copper sulfate, and performing desiccation thereto, wherein apurity of said copper sulfate is 99.99 wt % or higher and in which acontent of transition metals, such as Fe, Cr, and Ni, is 3 wtppm orless.
 2. High purity copper sulfate according to claim 1, wherein acontent of Ag and Cl in said copper sulfate is 1 wtppm or less,respectively.
 3. High purity copper sulfate according to claim 2,wherein a content of alkali metals, such as Na and K, and alkaline earthmetals, such as Ca and Mg, in said copper sulfate is 1 wtppm or less,respectively.
 4. High purity copper sulfate according to claim 3,wherein a content of an Si containing oxide in said copper sulfate is 10wtppm or less based on Si conversion.
 5. A copper sulfate having apurity of 99.99 wt % or higher.
 6. A copper sulfate according to claim5, wherein said copper sulfate has a content of transition metals, suchas Fe, Cr, and Ni, of 3 wtppm or less.
 7. A copper sulfate according toclaim 6, wherein said copper sulfate has a content of Ag and Cl of 1wtppm or less, respectively.
 8. A copper sulfate according to claim 7,wherein said copper sulfate has a content of alkali metals, such as Naand K, and alkaline earth metals, such as Ca and Mg, of 1 wtppm or less,respectively.
 9. A copper sulfate according to claim 8, wherein saidcopper sulfate has a content of an Si containing oxide of 10 wtppm orless based on Si conversion.
 10. A copper sulfate according to claim 5,wherein said copper sulfate has a content of Ag and Cl of 1 wtppm orless, respectively.
 11. A copper sulfate according to claim 5, whereinsaid copper sulfate has a content of alkali metals, such as Na and K,and alkaline earth metals, such as Ca and Mg, of 1 wtppm or less,respectively.
 12. A copper sulfate according to claim 5, wherein saidcopper sulfate has a content of an Si containing oxide of 10 wtppm orless based on Si conversion.
 13. An electrolytic solution forelectroplating copper to form a circuit or wiring of a semiconductordevice, comprising: copper sulfate having a purity of 99.99 wt % (4N) orhigher; said copper sulfate having a content of transition metals of 3wtppm or less; said copper sulfate having a content of Ag and Cl of 1wtppm or less, respectively; said copper sulfate having a content ofalkali metals and alkaline earth metals of 1 wtppm or less,respectively; and said copper sulfate having a content of a Sicontaining oxide of 10 wtppm or less based on Si conversion.
 14. Anelectrolytic solution according to claim 13, wherein said copper sulfatehas a content of nickel (Ni) of 1 wtppm or less and wherein said coppersulfate has a content of sodium (Na) of 0.3 wtppm or 0.4 wtppm.
 15. Anelectrolytic solution according to claim 14, wherein said copper sulfatehas a content of nickel (Ni) of 0.2 wtppm, and wherein said coppersulfate has a purity of 99.999 wt % (5N) or higher.
 16. A copper sulfateaccording to claim 8, wherein said copper sulfate has a content ofsodium (Na) of 0.3 wtppm or 0.4 wtppm.
 17. High purity copper sulfateaccording to claim 3, wherein said copper sulfate has a content ofsodium (Na) of 0.3 wtppm or 0.4 wtppm.